Process for manufacturing a dispersion of a vinylidene fluoride polymer

ABSTRACT

A process for manufacturing a dispersion of a vinylidene fluoride (VDF) thermoplastic polymer [polymer (F)], said process includes polymerizing VDF in an aqueous phase that includes: at least one surfactant selected from the group consisting of non-fluorinated surfactants [surfactant (HS)] and fluorinated surfactants having a molecular weight of less than 400 [surfactant (FS)]; and at least one functional (per)fluoropolyether (functional PFPE) comprising at least one (per)fluoropolyoxyalkylene chain [chain (R′ F )] and at least one functional group, said functional PFPE having a number average molecular weight of at least 1000 and a solubility in water of less than 1% by weight at 25° C., wherein said functional PFPE is present in the aqueous phase in an amount of 0.001 to 0.3 g/l.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. provisional application No.61/287,809 filed on Dec. 18, 2009 and to European application No.10164903.6 filed on Jun. 4, 2010, the whole content of each of theseapplications being incorporated herein by reference for all purposes.

TECHNICAL FIELD

The present invention pertains to a novel polymerization process formanufacturing vinylidene fluoride (VDF) polymer aqueous dispersionshaving particles with an average diameter from 0.1 to 0.3 micrometers,which are suitable for the formulation of paints, e.g. for highperformance external architectural coatings.

BACKGROUND ART

PVDF-based paints have been used since more than four decades for thecoil painting for architecture as they are capable to produce highperformance coatings.

Generally, the PVDF-based painting compositions comprise pigments,resins, generally acrylic resins, and various additives and can beapplied in a liquid form, when formulated in water or in particularsolvents, or in powder form.

Known high performance paints used for coatings in architecture are PVDFbased dispersions, having particles with an average diameter between 150to 350 nm prepared by emulsion polymerization in the presence of asurfactant formed of a mixture of perfluoroalkanoic acids having a chainlength between 7 and 13 carbon atoms and average molecular weight ofabout 480. Said surfactant is commercially known as Surflon™ S111 (AsahiGlass). The PVDF dispersion prepared by polymerization by using thisfluorosurfactants mixture is coagulated, and the polymer is then washed,dried in a spray dryer and then formulated with other additives toobtain the paint.

Nevertheless, recently, perfluoroalkanoic acids, in particular thosehaving 8 or more carbon atoms, have raised environmental concerns. Forinstance, perfluoroalkanoic acids have been found to showbioaccumulation. Accordingly, efforts are now devoted to phasing outfrom such compounds and methods have been developed to manufacturefluoropolymer products using alternative surfactants having a morefavourable toxicological profile.

Several approaches have been recently pursued to this aim, typicallyinvolving either non fluorinated, partially fluorinated or evenperfluorinated surfactants, these latter typically comprisingperfluoroalkyl linear or cyclic chains interrupted by one or morecatenary oxygen atoms, said chains having an ionic carboxylate group atone of its ends.

Nevertheless, all these surfactants do not possess suitable nucleatingbehaviour for providing VDF polymer particles having suitable sizes;these surfactants thus fail to enable tuning particle size of the latexin the range suitable for paints formulation.

DISCLOSURE OF INVENTION

It is thus an object of the present invention a process formanufacturing a dispersion of a vinylidene fluoride (VDF) thermoplasticpolymer [polymer (F)], said process comprising polymerizing VDF in anaqueous phase comprising:

-   -   at least one surfactant selected from the group consisting of        non-fluorinated surfactants [surfactant (HS)] and fluorinated        surfactants having a molecular weight of less than 400        [surfactant (FS)]; and    -   at least one functional (per)fluoropolyether (functional PFPE)        comprising at least one (per)fluoropolyoxyalkylene chain [chain        (R′_(F))] and at least one functional group, said functional        PFPE having a number average molecular weight of at least 1000        and a solubility in water of less than 1% by weight at 25° C.,        wherein said functional PFPE is present in the aqueous phase in        an amount of 0.001 to 0.3 g/l.

The Applicant has surprisingly found that in above mentioned process,the addition of a small amount of a high molecular weight functionalperfluoropolyether enables efficient nucleation and tuning of theaverage particle size of the polymer (F), while the hydrogenatedsurfactant and/or the low molecular weight fluorosurfactant ensureefficient colloidal stabilization of the dispersion.

More particularly, while average particle size of the particles ofpolymer (F) was found to be more or less insensitive of theconcentration of the surfactant (HS) or (FS), concentration offunctional PFPE can be efficiently used for tuning average particlessize of said polymer (F).

In other words, the combination of any of surfactant (HS) and (FS) withfunctional PFPE as above detailed advantageously enables separatingnucleating ability (due to the functional PFPE) from colloidalstabilization ability (due to the surfactant (HS) or (FS)).

The expression ‘thermoplastic’ is used herein to denote asemi-crystalline VDF polymer which can advantageously processed in themelt and which possesses typically a heat of fusion of more than 5 J/g,preferably more than 7 J/g, even more preferably 10 J/g, when measuredaccording to ASTM D 3418.

The vinylidene fluoride thermoplastic polymer [polymer (F)] ispreferably a polymer comprising:

(a′) at least 60% by moles, preferably at least 75% by moles, morepreferably 85% by moles of vinylidene fluoride (VDF);

(b′) optionally from 0.1 to 15%, preferably from 0.1 to 12%, morepreferably from 0.1 to 10% by moles of a fluorinated monomer differentfrom VDF; said fluorinate monomer being preferably selected in the groupconsisting of vinylfluoride (VF₁), chlorotrifluoroethylene (CTFE),hexafluoropropene (HFP), tetrafluoroethylene (TFE),perfluoromethylvinylether (MVE), trifluoroethylene (TrFE) and mixturestherefrom; and

(c′) optionally from 0.1 to 5%, by moles, preferably 0.1 to 3% by moles,more preferably 0.1 to 1% by moles, based on the total amount ofmonomers (a′) and (b′), of one or more hydrogenated comonomer(s).

The vinylidene fluoride polymer [polymer (F)] is more preferably apolymer consisting of:

(a′) at least 60% by moles, preferably at least 75% by moles, morepreferably 85% by moles of vinylidene fluoride (VDF);

(b′) optionally from 0.1 to 15%, preferably from 0.1 to 12%, morepreferably from 0.1 to 10% by moles of a fluorinated monomer differentfrom VDF; said fluorinate monomer being preferably selected in the groupconsisting of vinylfluoride (VF_(X)), chlorotrifluoroethylene (CTFE),hexafluoropropene (HFP), tetrafluoroethylene (TFE),perfluoromethylvinylether (MVE), trifluoroethylene (TrFE) and mixturestherefrom.

As non limitative examples of the VDF polymers of the present invention,mention can be notably made of homopolymer of VDF, VDF/TFE copolymer,VDF/TFE/HFP copolymer, VDF/TFE/CTFE copolymer, VDF/TFE/TrFE copolymer,VDF/CTFE copolymer, VDF/HFP copolymer, VDF/TFE/HFP/CTFE copolymer andthe like.

The process of the invention is particularly suitable for manufacturingVDF homopolymers.

The melt viscosity of the polymer (F), measured at 232° C. and 100 sec⁻¹of shear rate according to ASTM D3835, is advantageously of at least 5kpoise, preferably at least 10 kpoise.

The melt viscosity of the polymer (F), measured at 232° C. and 100 sec⁻¹of shear rate, is advantageously of at most 60 kpois, preferably at most40 kpoise, more preferably at most 35 kpoise.

The melt viscosity of VDF polymer is measured in accordance with ASTMtest No. D3835, run at 232° C., under a shear rate of 100 sec⁻¹.

The VDF polymer has a melting point of advantageously at least 120° C.,preferably at least 125° C., more preferably at least 130° C.

The VDF polymer has a melting point advantageously of at most 190° C.,preferably at most 185° C., more preferably at most 170° C.

The melting point (T_(m2)) can be determined by DSC, at a heating rateof 10° C./min, according to ASTM D 3418.

The surfactant can be a non-fluorinated surfactant, that is to say asurfactant which is free from fluorine.

The choice of the surfactant (HS) is not particularly critical.Generally anionic surfactants comprising at least one anionicfunctionality, preferably selected from the group consisting of:

wherein X_(a) is a hydrogen atom, a monovalent metal, preferably analkaline metal, or an ammonium group of formula —N(R′_(n))₄, whereinR′_(n), equal or different at each occurrence, is a hydrogen atom or aC₁-C₆ hydrocarbon group, preferably an alkyl group;

will be preferred.

Surfactants (HS) which can be used in the process of the invention canbe notably selected among alkanesulfonates, preferably selected fromlinear C₇-C₂₀ 1-alkanesulfonates, linear C₇-C₂₀ 2-alkanesulfonates, andlinear C₇-C₂₀ 1,2-alkanedisulfonates. These surfactants (HS) have beennotably described in U.S. Pat. No. 7,122,610 (ARKEMA INC) 27 Oct. 2005.Non limitative examples thereof are 1-octanesulfonates,2-octanesulfonates, 1,2-octanedisulfonates, 1-decanesulfonates,2-decanesulfonates, 1,2-decanedisulfonates, 1-dodecanesulfonates,2-dodecanesulfonates, 1,2-dodecanedisulfonates, and mixtures of any ofthese. As used herein, the term “alkanesulfonate(s)” and terms endingwith the term “sulfonate(s)” or “disulfonate(s),” such as those usedabove, refer to alkali metal, ammonium, or monoalkyl-, dialkyl-,trialkyl-, or tetraalkyl-substituted ammonium salts of alkanesulfonic oralkanedisulfonic acids. Sodium, potassium, and ammoniumalkanesulfonates, or mixtures of any of these, can be typically used.The use of ammonium ion as the counterion to the alkanesulfonate ion isgenerally preferred.

Surfactants (HS) which can be used in the process of the invention canbe notably further selected among alkylsulfates, preferably selectedfrom linear C₇-C₂₀ 1-alkylsulfates, linear C₇-C₂₀ 2-alkylsulfates, andlinear C₇-C₂₀ 1,2-alkyldisulfates. Non limitative examples thereof are1-octylsulfates, 2-octylsulfates, 1,2-octyldisulfates, 1-decylsulfates,2-decylsulfates, 1,2-decyldisulfates, 1-dodecylsulfates,2-dodecylsulfates, 1,2-dodecyldisulfates, and mixtures of any of these.As used herein, the term “alkylsulfate(s)” and terms ending with theterm “sulfate(s)” or “disulfate(s),” such as those used above, refer toalkali metal, ammonium, or monoalkyl-, dialkyl-, trialkyl-, ortetraalkyl-substituted ammonium salts of alkylsulfuric oralkyldisulfuric acids. Sodium, potassium, and ammonium alkylsulfates, ormixtures of any of these, can be typically used. The use of ammonium ionas the counterion to the alkylsulfate ion is generally preferred.

As an alternative, the surfactant can be a fluorine-containingsurfactant (i.e. a fluorinated surfactant) [surfactant (FS)], as abovedefined. The surfactant (FS) has a molecular weight of less than 400;the Applicant has found that only surfactants (FS) complying with thisrequirement are endowed with an appropriate toxicological profile whichmade them more acceptable from an environmental point of view.

It is nevertheless understood that mixture of one or more surfactant(HS) and one or more surfactant (FS) can be used in the process of theinvention.

It is generally preferred that the surfactant (FS) comprise at least onecatenary oxygen atom.

According to a first embodiment of the invention, the surfactant (FS)complies with formula (IA) here below:

R_(f)—(OCF₂CF₂)_(k-1)—O—CF₂—COOX_(a)  (IA)

wherein R_(f) is a C₁-C₃ perfluoroalkyl group comprising, optionally,one or more ether oxygen atoms, k is 2 or 3 and X_(a) is selected from amonovalent metal and an ammonium group of formula NR^(N) ₄, whereinR^(N), equal or different at each occurrence, is a hydrogen atom or aC₁-C₃ alkyl group.

A mixture of more than one surfactant (FS) having formula (IA) asdescribed above may also be used in this embodiment of the process ofthe invention.

The surfactant (FS) of this first embodiment preferably complies withformula (IIA) here below:

R_(f′)O—CF₂CF₂—O—CF₂—COOX_(a′)  (IIA)

wherein:

-   -   R_(f) ^(′) is a C₁-C₃ perfluoroalkyl group;    -   X_(a′) is selected from Li, Na, K, NH₄ and NR^(N′) ₄, wherein        R^(N′) is a C₁-C₃ alkyl group.

Still more preferably, the surfactant (FS) of the first embodimentcomplies with formula (IIIA) here below:

CF₃CF₂O—CF₂CF₂—O—CF₂—COOX_(a′)  (IIIA)

wherein X_(a′) has the same meaning as defined above.

According to a second embodiment of the invention, the surfactant (FS)complies with formula (IB) here below:

wherein:

-   -   X₁, X₂ and X₃, equal to or different from each other, are        independently selected from H, F and C₁-C₆ (per)fluoroalkyl        groups, optionally comprising one or more catenary or        non-catenary oxygen atoms,    -   R_(F) represents a divalent perfluorinated C₁-C₃ bridging group,    -   L represents a bond or a divalent group and    -   Y represents an anionic functionality, preferably selected from        the group consisting of:

wherein X_(a) is a hydrogen atom, a monovalent metal, preferably analkaline metal, or an ammonium group of formula —N(R′_(n))₄, whereinR′_(n), equal or different at each occurrence, is a hydrogen atom or aC₁-C₆ hydrocarbon group, preferably an alkyl group.

According to a first variant of this second embodiment of the invention,the surfactant (FS) complies with formula (IIB) here below:

wherein X₁, X₂, X₃, R_(F) and Y have the same meaning as defined above.The surfactant (FS) of formula (IIB) preferably complies with formula(IIIB) here below:

wherein X₁, X₂, X₃, R_(F) and X_(a) have the same meaning as definedabove. The surfactant (FS) of formula (IIIB) can comply with formula(IVB) here below:

wherein X′₁ and X′₂, equal to or different from each other, areindependently a fluorine atom, a —R′_(f) group or a —OR′_(f) group,wherein R^(′) _(f) is a C₁-C₃ perfluoroalkyl group, preferably with theproviso that at least one of X′₁ and X′₂ are different from fluorine,and R_(F) and X_(a) have the same meanings as defined above. Compoundsof formula (IV) as described above can be notably manufactured asdetailed in co-pending European Patent Applications No 08159936.7 and08168221.3. The surfactant (FS) having formula (IVB) of the firstvariant of this second embodiment preferably complies with formula (VB)here below:

wherein X′₁, X′₂, X′₃, X′₄, equal to or different each other, areindependently a fluorine atom, a —R′_(f) group or a —OR′_(f) group,wherein R^(′) _(f) is a C₁-C₃ perfluoroalkyl group.

Non limitative examples of surfactants (FS) having formula (VB) asdescribed above include, notably, the followings:

As an alternative, surfactant (FS) of formula (IIIB) can comply withformula (VIB) here below:

wherein X″₁ and X″₂, equal to or different from each other, areindependently a fluorine atom, a —R′_(f) group or a —OR′_(f) group,wherein R^(′) _(f) is a C₁-C₃ perfluoroalkyl group, and R_(F) and X_(a)have the same meanings as defined above. Compounds of formula (VIB) asdescribed above can be notably manufactured as detailed in co-pendingEuropean Patent Applications No 08159936.7 and 08168221.3.

The surfactant (FS) having formula (VIB) preferably complies withformula (VIIB) here below:

wherein X″₁, X″₂, X″₃, X″₄, equal to or different each other, areindependently a fluorine atom, a —R′_(f) group or a —OR′_(f) group,wherein R^(′) _(f) is a C₁-C₃ perfluoroalkyl group.

Non limitative examples of surfactants (FS) having formula (VIIB) asdescribed above include, notably, the followings:

According to a second variant of this second embodiment of theinvention, the surfactant (FS) complies with formula (VIIIB) here below:

wherein R_(F) and X_(a) have the same meanings as defined above, X*₁ andX*₂, equal to or different from each other, are independently a fluorineatom, a —R′_(f) group or a —OR′_(f) group, wherein R^(′) _(f) is a C₁-C₃perfluoroalkyl group, R*_(F) is a divalent fluorinated group and k is aninteger from 1 to 3. Compounds of formula (VIIIB) as described above canbe notably manufactured as detailed in co-pending European PatentApplications N° 08159936.7 and 08168221.3.

The surfactant (FS) of formula (VIIIB) preferably complies with formula(IXB) here below:

wherein R^(F) and X_(a) have the same meanings as defined above, X*₁ andX*₂, equal to or different from each other, are independently a fluorineatom, a —R′_(f) group or a —OR′_(f) group, wherein R^(′) _(f) is a C₁-C₃perfluoroalkyl group, R^(F) ₁ is a fluorine atom or a —CF₃ group and kis an integer from 1 to 3.

Among these compounds, surfactants (FS) having formulae (X) and (XI)here below:

wherein X_(a) has the meaning as defined above, have been foundparticularly useful in the process of the invention.

According to a third embodiment of the invention, the surfactant (FS)complies with formula:

R_(FS)−E-Y_(r)

wherein:

-   -   Y_(r) is an anionic functionality, preferably selected from the        group consisting of:

wherein X_(a) is a hydrogen atom, a monovalent metal, preferably analkaline metal, or an ammonium group of formula —N(R′_(n))₄, whereinR′_(n), equal or different at each occurrence, is a hydrogen atom or aC₁-C₆ hydrocarbon group, preferably an alkyl group;

-   -   E is a C₄-C₂₄ hydrocarbon non fluorinated divalent group,        possibly comprising one or more catenary oxygen atom(s); and    -   R_(FS) is a —OR^(FS) _(f) group, a —N(R^(FS) _(f))₂, or a        —OAr(R^(FS) _(f))_(r) group, wherein R^(FS) f, equal to or        different from each other at each occurrence, is a C₁-C₆        perfluoroalkyl group, Ar is an aromatic moiety (e.g. a phenyl        group), and r is an integer of 1 to 3.

Examples of surfactants (FS) of this third embodiment are notablydisclosed in US 2008149878 26 Jun. 2008.

The surfactant (FS) according to this third embodiment of the inventionpreferably complies with formula:

R_(FS)(CH₂)_(n)SO₃X_(r)

wherein:

-   -   X_(r) is a hydrogen atom, a monovalent metal, preferably an        alkaline metal, or an ammonium group of formula —N(R′_(n))₄,        wherein R′_(n), equal or different at each occurrence, is a        hydrogen atom or a C₁-C₆ hydrocarbon group, preferably an alkyl        group;    -   n is an integer of 4 to 20; and    -   R_(FS) is a —OR^(FS) _(f) group, a —N(R^(FS) _(f))₂, or a        —OAr(R^(FS) _(f))_(r) group, wherein R^(FS) f, equal to or        different from each other at each occurrence, is a C₁-C₆        perfluoroalkyl group, Ar is an aromatic moiety (e.g. a phenyl        group), and r is an integer of 1 to 3.

The surfactant (FS) of this third embodiment more preferably complieswith formula R_(FS)(CH₂)_(n)SO₃X_(r), with R_(FS) being selected fromthe group consisting of —OCF₃, —N(CF₃)₂ and

The total amount of surfactant(s) (FS) and/or (HS) is not particularlylimited and will be advantageously selected to the aim of achievingsuitable colloidal stability. In general, concentrations of surfactant(FS) and/or (HS) of from 0.01 to 10 g/l in the aqueous phase will bepreferred.

The aqueous phase of the process of the present invention also comprisesat least one functional (per)fluoropolyether (functional PFPE)comprising at least one (per)fluoropolyoxyalkylene chain [chain(R′_(F))] and at least one functional group, said functional PFPE havinga number average molecular weight of at least 1000 and a solubility inwater of less than 1% by weight at 25° C.

The Applicant has surprisingly found that when a functional PFPE is usedfailing to satisfy above mentioned requirements of molecular weight andsolubility, its nucleating activity is not effective and technicaleffects of the invention are not achieved.

On the contrary, a functional PFPE fulfilling said molecular weight andsaid solubility features has been found to effectively perform in themethod of the present invention to produce particles of the requiredsize thanks to its outstanding nucleating activity.

The functional PFPE has a solubility in water of preferably less than0.5%, more preferably of less than 0.1% by weight at 25° C.

The (per)fluoropolyoxyalkylene chain [chain (R′_(F))] of the functionalPFPE typically comprises one or more recurring units R″ having generalformula —(CF₂)_(j)—CFZO—, wherein Z is selected from a fluorine atom anda C₁-C₅ (per)fluoro(oxy)alkyl group and j is an integer comprisedbetween 0 and 3, the recurring units being generally statisticallydistributed along the (per)fluoropolyoxyalkylene chain.

The functional PFPE has a number average molecular weight of preferablyat least 1300, more preferably at least 1500.

The “number average molecular weight” is hereby expressed by the formulahere below:

$M_{n} = \frac{\sum\; {M_{i} \cdot N_{i}}}{\sum\; N_{i}}$

wherein N_(i) represents the number of molecules having averagemolecular weight M_(i).

The functional PFPE preferably comprises at least one functional groupselected from carboxylic acid, phosphonic acid and sulphonic acidgroups, in their acid or salt form.

The functional PFPE more preferably complies with formula (XII) herebelow:

T₁-(CFW₁)_(p1)—O—R_(F)—(CFW₂)_(p2)-T₂  (XII)

wherein:

-   -   R_(F) is a (per)fluoropolyoxyalkylene chain [chain (R′_(F))], as        defined above, such that the number average molecular weight of        the functional PFPE is at least 1000, preferably at least 1300,        more preferably at least 1500;    -   T₁ and T₂, equal to or different from each other, are selected        from:

i) functional end-groups selected from carboxylic acid, phosphonic acidand sulphonic acid groups, in their acid or salt form, and

ii) non-functional end-groups selected from a fluorine atom, a chlorineatom and a C₁-C₃ (per)fluoroalkyl group comprising, optionally, one ormore chlorine atoms,

with the proviso that at least one of T₁ and T₂ is a functionalend-group as defined above;

-   -   W₁ and W₂, equal to or different from each other, independently        represent a fluorine atom or a —CF₃ group;    -   p₁ and p₂, equal to or different from each other, are        independently integers comprised between 1 and 3, preferably        being equal to 1 when W₁ and/or W₂ are —CF₃ groups.

The aqueous phase preferably comprises at least one functional PFPEcomplying with formula (XII) as described above wherein both T₁ and T₂are functional end-groups as defined above (bifunctional PFPE).

Non-limitative examples of suitable bifunctional PFPEs include, notably,those complying with formula (XIII) here below:

X_(p)OOC—CFW₁—O—R_(F)—CFW₂—COOX_(p)  (XIII)

wherein:

-   -   R_(F) is a (per)fluoropolyoxyalkylene chain [chain (R′_(F))] as        defined above such that the number average molecular weight of        the bifunctional PFPE is at least 1000, preferably at least        1300, more preferably at least 1500;    -   W₁ and W₂, equal to or different from each other, have the same        meaning as defined above;    -   X_(p), equal to or different from each other, is a hydrogen        atom, a monovalent metal, preferably an alkaline metal, or an        ammonium group of formula —N(R′_(n))₄, wherein R′_(n), equal or        different at each occurrence, is a hydrogen atom or a C₁-C₆        hydrocarbon group, preferably an alkyl group.

More preferred aqueous phases comprise at least one bifunctional PFPEcomplying with formula (XIV) here below:

X_(p)OOC—CF₂—O—(CF₂)_(n′)(CF₂CF₂O)_(m′)—CF₂—COOX_(p)  (XIV)

wherein n′ and m′ are independently integers >0 such that the numberaverage molecular weight of the bifunctional PFPE is at least 1000,preferably at least 1300, more preferably at least 1500, the recurringunits being generally statistically distributed along theperfluoropolyoxyalkylene chain, and X_(p) has the meaning as abovedefined.

The functional perfluoropolyether is present in the aqueous phase in anamount of 0.001 to 0.3 g/l.

Preferably, the functional PFPE is present in an amount of 0.001 to 0.15g/l, preferably of 0.001 to 0.1 g/l in the aqueous phase.

The Applicant has surprisingly found that, while the functional PFPEalone cannot provide with adequate stabilization during polymerization,by addition of functional PFPE to the surfactant (FS) as above detailedin above mentioned amounts it is advantageously possible to fine tuningthe average molecular weight of the polymer (F) and simultaneouslyachieving high solid concentrations and outstanding colloidal stability.

By selecting a concentration of functional PFPE of from 0.001 to 0.1g/l, it is advantageously possible to obtain a dispersion of polymer (F)having an average particle size of from 300 to 150 nm.

To the aim of manufacturing polymer (F) dispersions suitable forformulating architectural coating paints, i.e. dispersions with averageparticles size of 250 to 300 nm, the amount of functional PFPE will beselected in the range of 0.001 to 0.005 g/l.

The polymerization process of the invention is typically started by aninitiator. Suitable initiators include any of the initiators known forinitiating a free radical polymerization of vinylidene fluoride.

Non-limitative examples of suitable initiators include, notably,inorganic initiators and peroxide initiators.

Representative examples of inorganic initiators include, notably,ammonium-, alkali- or earth alkali-salts of persulfates or (per)manganicacids. A persulfate initiator, e.g. ammonium persulfate, can be used onits own or may be used in combination with a reducing agent. Suitablereducing agents include bisulfites such as, e.g., ammonium bisulfite orsodium metabisulfite, thiosulfates such as, e.g., ammonium, potassium orsodium thiosulfate, hydrazines, azodicarboxylates andazodicarboxyldiamide. Further reducing agents which may be used includesodium formaldehyde sulfoxylate (Rongalite) or fluoroalkyl sulfinates asdisclosed in U.S. Pat. No. 5,285,002 (MINNESOTA MINING AND MANUFACTURINGCO.) Aug. 2, 1994. The reducing agent typically reduces the half-lifetime of the persulfate initiator. Additionally, a metal salt catalystsuch as, e.g., copper, iron or silver salts may be added.

Representative examples of peroxide initiators include, notably,hydrogen peroxide, sodium or barium peroxide, diacylperoxides such as,e.g., diacetylperoxide, disuccinyl peroxide, dipropionylperoxide,dibutyrylperoxide, dibenzoylperoxide, di-tert-butylperoxide,benzoylacetylperoxide, diglutaric acid peroxide and dilaurylperoxide,and further per-acids and salts thereof such as, e.g., ammonium, sodiumor potassium salts. Specific examples of per-acids include, notably,peracetic acid. Esters of the peracid can be used as well and examplesthereof include tert-butylperoxyacetate and tert-butylperoxypivalate.

The amount of initiator typically ranges between 0.01% and 1% by weight,preferably between 0.01 and 0.5% by weight with respect to the weight ofthe polymer (F) to be produced.

The polymerization process may be carried out in the presence of othermaterials such as, notably, chain-transfer agents. Non-limitativeexamples of chain transfer agents suitable for the purpose of theprocess of the invention include, notably, compounds of formulaR_(f)(I)_(x)(Br)_(y), wherein R_(f) is a C₁-C₈ (per)fluoro(chloro)alkylgroup, x and y are independently integers between 0 and 2, the (x+y) sumbeing comprised between 1 and 2, such as, e.g.,1,4-diiodoperfluorobutane. Further chain-transfer agents which may beused include, notably, C₁-C₅ alkanes such as, e.g., ethane, propane andn-pentane, halogenated hydrocarbons such as, e.g., CCl₄, CHCl₃, CH₂Cl₂,hydrofluorocarbon compounds such as, e.g., CH₂F—CF₃ (R134a), ethers suchas, e.g., dimethyl ether and methyl tert-butyl ether and esters such as,e.g., ethyl acetate and malonic esters.

The process of the invention generally comprises the following steps:

a) feeding an aqueous solution of the surfactant (FS) and/or (HS) intothe polymerization reactor, possibly in combination with deionizedwater, so as to achieve the required concentration of surfactant (FS)and/or in the aqueous phase;

b) adding the required amount of functional PFPE to said aqueous phase;

c) optionally adding into the aqueous medium chain transfer agent(s),stabilizer(s) and/or other polymerization additive(s);

d) adding vinylidene fluoride, possibly in combination with othercopolymerizable monomers, if required;

d) adding the polymerization initiator and, optionally, during thepolymerization, further adding additional amounts of VDF monomer and/orcomonomers, initiators, transfer agents;

f) recovering from the reactor the polymer (F) dispersion.

Polymerization is generally carried out at a pressure of at least 350psi, preferably of at least 400 psi, more preferably of at least 500psi.

Polymerization can be carried out at a temperature of at least 50° C.,preferably of at least 60° C., more preferably of at least 80° C.

Upper temperature is not particularly limited, provided that an aqueousphase is maintained in polymerization conditions. Generally temperaturewill not exceed 130° C., preferably 125° C.

The invention further pertains to an aqueous dispersion of polymer (F),as above described, said aqueous dispersion comprising at least onesurfactant (FS), and/or one surfactant (HS) as above detailed, and atleast one functional PFPE as above detailed.

The aqueous dispersion of the invention is advantageously obtained fromthe process of the invention.

Still an object of the invention is the use of the dispersion, as abovedetailed, for the manufacture of paints.

With the aim of being used for formulating paints, the aqueousdispersions of polymer (F) as above detailed is generally coagulated soas to obtain a dry powder of polymer (F).

Said polymer (F) is generally dispersed in a suitable organic dispersingmedium, typically a latent or intermediate solvent of polymer (F).

An intermediate solvent for the polymer (F) is a solvent which does notdissolve or substantially swell the polymer (F) at 25° C., whichsolvates polymer (F) at its boiling point, and retains polymer (F) insolvated form, i.e. in solution, upon cooling.

A latent solvent for the polymer (F) is a solvent which does notdissolve or substantially swell polymer (F) at 25° C., which solvatespolymer (F) at its boiling point, but on cooling, polymer (F)precipitates.

Latent solvents and intermediate solvents can be used alone or inadmixture. Mixtures of one or more than one latent solvent with one ormore than one intermediate solvent can be used.

Intermediate solvents suitable for polymer (F) paint formulations arenotably butyrolactone, isophorone and carbitol acetate.

Latent solvents suitable for suitable for polymer (F) paint formulationsare notably methyl isobutyl ketone, n-butyl acetate, cyclohexanone,diacetone alcohol, diisobutyl ketone, ethyl acetoacetate, triethylphosphate, propylene carbonate, triacetin (also known as1,3-diacetyloxypropan-2-yl acetate), dimethyl phthalate, glycol ethersbased on ethylene glycol, diethylene glycol and propylene glycol, andglycol ether acetates based on ethylene glycol, diethylene glycol andpropylene glycol.

Non limitative examples of glycol ethers based on ethylene glycol,diethylene glycol and propylene glycol are notably ethylene glycolmonomethyl ether, ethylene glycol monoethyl ether, ethylene glycolmonopropyl ether, ethylene glycol monobutyl ether, ethylene glycoldimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutylether, diethylene glycol monomethyl ether, diethylene glycol monoethylether, diethylene glycol mono-n-butyl ether, propylene glycol methylether, propylene glycol dimethyl ether, propylene glycol n-propyl ether.

Non limitative examples of glycol ether acetates based on ethyleneglycol, diethylene glycol and propylene glycol are notably ethyleneglycol methyl ether acetate, ethylene glycol monethyl ether acetate,ethylene glycol monobutyl ether acetate, propylene glycol methyl etheracetate.

Non-solvents for polymer (F) such as methanol, hexane, toluene, ethanoland xylene may also be used in combination with latent solvent and/orintermediate solvent for special purpose, e.g. for controlling paintrheology, in particular for spray coating.

Typically, the polymer (F) paint formulation will comprise additionalingredients, including notably, (meth)acrylic resins, pigments, fillers,stabilizers and the like.

The invention will be now described with reference to the followingexamples, whose purpose is merely illustrative and not limitative of thescope of the invention.

Should the disclosure of any patents, patent applications, andpublications which are incorporated herein by reference conflict withthe description of the present application to the extent that it mayrender a term unclear, the present description shall take precedence.

EXAMPLE 1: GENERAL POLYMERIZATION PROCEDURE WITH COMPOUND CF₃CF₂O—CF₂CF₂—O—CF₂—COOXA′ (IIIA), XA′=NH₄

In a typical polymerization run, the 7.57 L reactor was charged with5289 g of deionized water, 86 g of 10% w/w aqueous solution ofsurfactant (IIIA), with X_(a)=NH₄, 5.4 mg of a functional PFPE complyingwith formula HOOC—CF₂—O—(CF₂)_(n″)(CF₂CF₂O)_(m″)—CF₂—COOH, with n″ andm″ such that the number averaged molecular weight is about 1800 (saidfunctional PFPE having a solubility of less than 0.1% wt in water at 25°C.), and 4 g of wax.

The reactor was heated to 100° C. and vented for 2 min. The temperaturewas increased to 122.5 C and the reactor was pressurized with vinylidenefluoride (VDF) to 650 psi. 24.4 mL of pure di-tert-butyl peroxide wereadded to the reactor to initiate polymerization, and the pressure wasmaintained at 650 psi throughout polymerization.

Upon reaching conversion (2298 g of consumed monomer), the monomer feedand agitation were interrupted, the reactor was cooled, and the polymerlatex was collected from the reactor.

The latex was filtered to collect eventual coagulum and the reactor wasinspected to determine the amount of build-up (i.e. polymer stuck ontothe agitation blade and reactor walls).

EXAMPLE 2: GENERAL POLYMERIZATION PROCEDURE WITH COMPOUND

Xa′=NH₄

In a typical polymerization run, the 7.57 L reactor was charged with5241 g of deionized water, 134 g of a 10% w/w aqueous solution ofsurfactant (XB), with X_(a)=NH₄, 5.4 mg of same functional PFPE of Ex.1, and 4 g of wax. The reactor was heated to 100° C. and vented for 2min.

The temperature was increased to 122.5° C. and the reactor waspressurized with vinyledene fluoride (VDF) to 650 psi. 24.4 mL of puredi-tert-butyl peroxide were added to the reactor to initiatepolymerization, and the pressure was maintained at 650 psi throughoutpolymerization. Upon reaching target conversion (2298 g of consumedmonomer), the monomer feed and agitation were interrupted, the reactorwas cooled, and the polymer latex was collected from the reactor. Thelatex was filtered to collect eventual coagulum and the reactor wasinspected to determine the amount of build-up.

Results of polymerization runs are summarized in the following tables,including reference runs carried out in the absence of functional PFPE.

TABLE 1 Conc. (IIIA) Conc. of Solid Latex X_(a) = NH₄ funct PFPE APS^(§)content Coagulum Build up viscosity Run (g/l) (g/l) (nm) (% w/w) (g) (g)(kPoise) 1-a 0.60 none 585 10.9 0 1784 34.014 comp 1-b 1.00 none 48326.82 467.0 215 32.082 comp 1-c 2.00 none 328 29.06 14.8 58 31.598 comp1-d 1.60 0.001 287 29.46 35.0 47 32.158 1-e 1.20 0.001 288 28.75 182.0133 30.968 1-f 1.00 0.001 284 28.6 224.0 114 32.979 1-g 1.00 0.002 25129.35 93.4 43 32.754 1-h 1.00 0.008 192 30.7 14.0 78 n.d. 1-i 1.00 0.15120 27.16 17.0 40 28.029 1-j 1.00 0.30 108 30.12 12.0 19 24.028^(§)average primary particle size

Data hereby provided well demonstrate that surfactant (FS) alone cannotprovide for VDF polymers having average particle sizes ranging from 100to 300 nm, as required for paint formulation.

On the contrary, addition of limited amount of functional PFPE enabledefficient tuning of particle size. Examples 1-d to 1-f show that averageparticle size is substantially identical when changing concentration ofsurfactant (FS). On the contrary, runs 1-f to 1-g, well demonstrate theability of obtaining VDF polymer dispersions with average sizes from 100to 300 nm by changing concentration of the functional PFPE.

TABLE 2 Conc. (XB) Conc. of Solid Latex X′_(a) = NH₄ funct PFPE APScontent Coagulum Build-up viscosity Run (g/l) (g/l) (nm) (% w/w) (g) (g)(kPoise) 2-b 2.50 0.001 282 28.13 163 169 32.199

COMPARATIVE EXAMPLE 3—POLYMERIZATION WITH COMPOUND

Xa′=NH₄ and Functional PFPE Having Low Molecular Weight and HighSolubility

Same procedure as detailed in Example 2 was followed but using asfunctional PFPE a compound complying with formulaH₄NOOC—CF₂—O—(CF₂)_(n″)(CF₂CF₂O)_(m″)—CF₂—COONH₄, with n″ and m″ suchthat the number averaged molecular weight is about 460 and having asolubility of more than 20% wt in water at 25° C. By combining saidfunctional PFPE with compound (XB) with X′_(a)═NH₄, it was not possibleto efficiently nucleating and stabilizing the dispersion. Huge build-upof polymer onto the reactor walls, low solids and extremely largeparticles were obtained in these conditions. Results are summarized inTable 3 herein below.

TABLE 3 Conc. (XB) Conc. of Solid Latex X′_(a) = NH₄ funct PFPE APScontent Coagulum Build-up viscosity Run (g/l) (g/l) (nm) (% w/w) (g) (g)(kPoise) 3-a 0.50 1.5 1046 0.96 0 395 n.d. comp

EXAMPLE 4: GENERAL POLYMERIZATION PROCEDURE WITH COMPOUND 1OCTYL-SULFONATE

A 7.5-liter stainless steel horizontal reactor, equipped with a paddleagitator, was charged with a total of 5.375 kg of deionized water andaqueous solution of a surfactant mixture containing 1-octanesulfonateand same functional PFPE used in example 1, such that the concentrationof 1-octanesulfonate was 1.2 g/L and of the functional PFPE was 13 mg/Lin the aqueous phase of the reactor. In addition, 4 g of a hydrocarbonwax melting at 50 to 60° C. was added. The reactor was sealed anddeaerated by heating with agitation to 100° C., then venting steam andair from the reactor for two minutes. The reactor was then heated to122.5° C. Sufficient vinylidene fluoride monomer was introduced from acylinder to bring the reactor pressure to 650 psig (45 bar). Then 21.5mL of di-tert-butyl peroxide (DTBP) was pumped into the reactor toinitiate the polymerization reaction. After an induction period ofapproximately 15 minutes, the reactor pressure decreased slightly,indicating initiation. Vinylidene fluoride then was continuously addedas needed to maintain the reactor pressure at 650 psig (45 bar) whilethe reactor temperature was maintained at 122.5° C. by pumping water andethylene glycol through the reactor jacket. After about 262 minutes,when a total of 2298 g of vinylidene fluoride had been fed to thereactor, the monomer feed was stopped. In order to maximize yield, thesystem was allowed to continue reacting until the reactor pressure wasdecreased to about 150 psig (about 10 bar). At that point, the reactorwas cooled, the unreacted vinylidene fluoride was vented, and the latexwas drained from the reactor. The resulting latex was screened throughan 80 mesh screen to remove precoagulated large particles. In addition,the reactor wall was cleaned mechanically to remove any adheringprecoagulated large particles. A coagulation loss (defined as thepercentage of the original 2298 g of vinylidene fluoride monomer thatwas recovered as precoagulated large particles) of 4.1% was found. Thescreened latex was analyzed by laser light scattering and found to havean average latex particle size of 262 nm.

EXAMPLE 5: GENERAL POLYMERIZATION PROCEDURE WITH COMPOUND SODIUM OCTYLSULPHATE

The polymerization procedure in Example 4 was repeated, with thesurfactant system consisting of sodium octyl sulfate (Texapon 842, fromCognis) at 1.2 g/L and same functional PFPE of example 1 at 13 mg/L inthe aqueous phase of the reactor. After about 436 minutes, when a totalof 2298 g of vinylidene fluoride had been fed to the reactor, themonomer feed was stopped and a similar react down procedure wasfollowed. The resulting latex was found to have a coagulation loss of8.8% and an average particle size of 208 nm.

COMPARATIVE EXAMPLE 6: GENERAL POLYMERIZATION PROCEDURE WITH COMPOUND 1OCTYL-SULFONATE WITHOUT ANY ADDED FUNCTIONAL PFPE

The polymerization procedure in Example 4 was followed, with thesurfactant system consisting of only sodium 1-octanesulfonate at 1.2 g/Lin the aqueous phase of the reactor, with no functional PFPE added.After about 274 minutes, when a total of 1976 g of vinylidene fluoridehad been fed to the reactor, the monomer feed was stopped and a similarreact down procedure was followed. The resulting latex was found to havea coagulation loss of 44.8% and an average particle size of 481 nm.

COMPARATIVE EXAMPLE 7: GENERAL POLYMERIZATION PROCEDURE WITH COMPOUNDSODIUM OCTYL SULFATE WITHOUT ANY ADDED FUNCTIONAL PFPE

The polymerization procedure of Example 4 was followed, with thesurfactant system consisting of only sodium octyl sulfate at 1.2 g/L inthe aqueous phase of the reactor. After about 428 minutes, when a totalof 2298 g of vinylidene fluoride had been fed to the reactor, themonomer feed was stopped and a similar react down procedure wasfollowed. The resulting latex was found to have a coagulation loss of36.7% and an average particle size of 412 nm.

1.-14. (canceled)
 15. A process for manufacturing a dispersion of avinylidene fluoride (VDF) thermoplastic polymer [polymer (F)], saidprocess comprising polymerizing VDF in an aqueous phase comprising: atleast one surfactant selected from the group consisting ofnon-fluorinated surfactants [surfactant (HS)] and fluorinatedsurfactants having a molecular weight of less than 400 [surfactant (FS)]selected from the group consisting of: surfactant (FS) complying withformula (IA) here below:R_(f)—(OCF₂CF₂)_(k-1)—O—CF₂—COOX_(a)  (IA) wherein R_(f) is a C₁-C₃perfluoroalkyl group comprising, optionally, one or more ether oxygenatoms, k is 2 or 3 and X_(a) is selected from a monovalent metal and anammonium group of formula NR^(N) ₄, wherein R^(N), equal or different ateach occurrence, is a hydrogen atom or a C₁-C₃ alkyl group; andsurfactant (FS) complying with formula:R_(FS)-E-Y_(r) wherein: Y_(r) is an anionic functionality; wherein E isa C₄-C₂₄ hydrocarbon non fluorinated divalent group, possibly comprisingone or more catenary oxygen atom(s); and wherein R_(FS) is a —OR^(FS)_(f) group, a —N(R^(FS) _(f))₂, or a —OAr(R^(FS) _(f))_(r) group,wherein R^(FS) _(f), equal to or different from each other at eachoccurrence, is a C₁-C₆ perfluoroalkyl group, Ar is an aromatic moiety(e.g. a phenyl group), and r is an integer of 1 to 3; and at least onefunctional (per)fluoropolyether (functional PFPE) comprising at leastone (per)fluoropolyoxyalkylene chain [chain (R′_(F))] and at least onefunctional group, said functional PFPE having a number average molecularweight of at least 1000 and a solubility in water of less than 1% byweight at 25° C., wherein said functional PFPE is present in the aqueousphase in an amount of 0.001 to 0.3 g/l.
 16. The process of claim 15,wherein the surfactant is a surfactant (FS) complying with formula (IA)here below:R_(f)—(OCF₂CF₂)_(k-1)—O—CF₂—COOX_(a)  (IA) wherein R_(f) is a C₁-C₃perfluoroalkyl group comprising, optionally, one or more ether oxygenatoms, k is 2 or 3 and X_(a) is selected from a monovalent metal and anammonium group of formula NR^(N) ₄, wherein R^(N), equal or different ateach occurrence, is a hydrogen atom or a C₁-C₃ alkyl group.
 17. Theprocess of claim 16, wherein the surfactant (FS) complies with formula(IIIA) here below:CF₃CF₂O—CF₂CF₂—O—CF₂—COOX_(a′)  (IIIA) wherein X_(u′) is selected fromLi, Na, K, NH₄ and NR^(N′) ₄, wherein R^(N′) is a C₁-C₃ alkyl group. 18.The process of claim 15, wherein the surfactant is a surfactant (FS)complying with formula:R_(FS)-E-Y_(r) wherein: Y_(r) is an anionic functionality selected fromthe group consisting of:

wherein X_(a) is a hydrogen atom, a monovalent metal, or an ammoniumgroup of formula —N(R′_(n))₄, wherein R′_(n), equal or different at eachoccurrence, is a hydrogen atom or a C₁-C₆ hydrocarbon group; wherein Eis a C₄-C₂₄ hydrocarbon non fluorinated divalent group, possiblycomprising one or more catenary oxygen atom(s); and wherein R_(FS) is a—OR^(FS) _(f) group, a —N(R^(FS) _(f))₂, or a —OAr(R^(FS) _(f)), group,wherein R^(FS) _(f), equal to or different from each other at eachoccurrence, is a C₁-C₆ perfluoroalkyl group, Ar is an aromatic moiety(e.g. a phenyl group), and r is an integer of 1 to
 3. 19. The process ofclaim 18, wherein the surfactant (FS) complies with formula:R_(FS)(CH₂)_(n)SO₃X_(r) wherein: X_(r) is a hydrogen atom, a monovalentmetal, or an ammonium group of formula —N(R′_(n))₄, wherein R′_(n),equal or different at each occurrence, is a hydrogen atom or a C₁-C₆hydrocarbon group; wherein n is an integer of 4 to 20; and whereinR_(FS) is a —OR^(FS) _(f) group, a —N(R^(FS) _(f))₂, or a —OAr(R^(FS)_(f))_(r) group, wherein R^(FS) _(f), equal to or different from eachother at each occurrence, is a C₁-C₆ perfluoroalkyl group, Ar is anaromatic moiety (e.g. a phenyl group), and r is an integer of 1 to 3.20. The process according to claim 15, wherein said at least onesurfactant is selected from the group consisting of non-fluorinatedsurfactants [surfactants (HS)].
 21. The process of claim 20, whereinsaid surfactants (HS) are selected from the group consisting of:alkanesulfonates and alkylsulfates.
 22. The process of claim 15, whereinthe functional PFPE complies with formula (XII) here below:T₁-(CFW₁)_(p1)—R_(F)—(CFW₂)_(p2)-T₂  (XII) wherein: R_(F) is a(per)fluoropolyoxyalkylene chain [chain (R′_(F))] such that the numberaverage molecular weight of the functional PFPE is at least 1000;wherein T₁ and T₂, equal to or different from each other, are selectedfrom: functional end-groups selected from carboxylic acid, phosphoricacid and sulphonic acid groups, in their acid or salt form, andnon-functional end-groups selected from a fluorine atom, a chlorine atomand a C₁-C₃ (per)fluoroalkyl group comprising, optionally, one or morechlorine atoms, with the proviso that at least one of T₁ and T₂ is afunctional end-group as defined above; wherein W₁ and W₂, equal to ordifferent from each other, independently represent a fluorine atom or a—CF₃ group; and wherein p₁ and p₂, equal to or different from eachother, are independently integers comprised between 1 and
 3. 23. Theprocess of claim 22, wherein the functional PFPE complies with formula(XIV) here below:X_(p)OOC—CF₂—O—(CF₂)_(n′)(CF₂CF₂O)_(m′)—CF₂—COOX_(p)  (XIV) wherein n′and m′ are independently integers >0 such that the number averagemolecular weight of the functional PFPE is at least 1000, the recurringunits being generally statistically distributed along theperfluoropolyoxyalkylene chain, and X_(p), equal to or different fromeach other, is a hydrogen atom, a monovalent metal, or an ammonium groupof formula —N(R′_(n))₄, wherein R′_(n), equal or different at eachoccurrence, is a hydrogen atom or a C₁-C₆ hydrocarbon group.
 24. Theprocess of claim 18, wherein X_(a) is an alkaline metal.
 25. The processof claim 19, wherein X_(r) is an alkaline metal.
 26. The process ofclaim 21, wherein said surfactants (HS) are alkanesulfonates selectedfrom the group consisting of linear C₇-C₂₀ 1-alkanesulfonates, linearC₇-C₂₀ 2-alkanesulfonates, and linear C₇-C₂₀ 1,2-alkanedisulfonates, andmixtures thereof.
 27. The process of claim 21, wherein said surfactants(HS) are alkylsulfates selected from the group consisting of linearC₇-C₂₀ 1-alkylsulfates, linear C₇-C₂₀ 2-alkylsulfates, and linear C₇-C₂₀1,2-alkyldisulfates, and mixtures thereof.
 28. The process of claim 22,wherein p₁ and p₂ are 1 when W₁ and/or W₂ are —CF₃ groups.
 29. Theprocess of claim 23, wherein X_(p) is an alkaline metal.